The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work [1] we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling. Our predictions are in good agreement with recent measurements [2] which demonstrate strong coupling with spin-photon coupling rates of more than 10 MHz. Furthermore, we employ input-output theory to identify observable signatures in the cavity output field, which can provide guidance to the experimental search for strong coupling in such systems and opens the way to cavity-based readout of the spin qubit.